The present invention relates to network interfacing and, more particularly, to a novel network transceiver that performs handshaking to establish synchronization between a repeater and a physical layer device at different data rates.
A Local Area Network, or (LAN), is a communications systems that provides a connection among a number of independent computing stations within a small area, such as a single building or group of adjacent buildings. One type of network structure uses one or more repeaters in a star typology, with each repeater having several ports. A data packet received at one port is retransmitted to all other ports of the repeater. Each repeater in turn restores timing and amplitude degradation of data packets received at one port and retransmits the packets to all other ports.
Traditional Ethernet networks (10BASE-T) operate at 10 Mb/s Ethernet protocol, as described by IEEE Standard 802.3; the majority of Ethernet interfaces currently operate at this data rate. However, a newer Ethernet network, under IEEE standard 802.3 u, accomplishes the faster operation of 100 BASE-T systems, at 125 Mb/s using unshielded twisted pair (UTP) physical media. The 100 BASE-T standard defines operation over two pairs of category 5 UTP (100 BASE-TX) or category 3 UTP, 100 BASE-FX, covered by the 100 BASE-T standard, allows operation over dual fiber optic cabling.
Ethernet protocol provides for a Media Access Control (MAC), enabling network interface devices at each network node to share accesses to the network medium. A Media Independent Interface, or MII, connects the MAC to a physical layer (PHY) transceiver configured for a particular network medium, e.g., 10 BASE-T, 100 BASE-FX, or 100 BASE-TX. The physical layer transceiver is configured for converting the MII protocol signals output by the MAC into analog network signals, such as Multiple Layer Transition-3 (MLT-3) signals for 100 Mb/s Ethernet networks, or Manchester-encoded signals for 10 Mb/s Ethernet networks. (Networks often use several PHY devices operating over different media types.)
Ethernet switches have multiple interfaces, each capable of either 10 Mb/s or 125 Mb/s operation, or potentially another data rate operation, and are able to be connected in communication with a link partner operating at a corresponding data rate. Because a switch allows multiple simultaneous traffic on its ports, it is possible to allow the ports to operate at different speeds relative to each other. A repeater, on the other hand, is configured to operate at only a single data rate. A 10 Mb/s repeater, for example, cannot be placed in communication with a link partner operating at 100 Mb/s.
Thus, in order to communicate with link partners operating at different data rates, several repeaters having corresponding data rates should be used. Alternatively, several repeaters may be integrated into a single repeater device having repeater cores running at different speeds. For example, for link partners operating at 100 Mb/s and 10 Mb/s, each PHY device should be switched between a 100 Mb/s repeater and a 10 Mb/s repeater.
When a PHY device changes its speed, synchronization should be established between the PHY device and a repeater to make sure that the PHY device is mapped to the repeater capable of communicating at required speed. Therefore, it would be desirable to provide a repeater/PHY device handshake mechanism that insures that a PHY device is mapped to a proper repeater.
The invention provides a novel method of operating physical layer devices in a local area network, such as one conforming to Ethernet protocol, in which there are a plurality of repeaters of respectively different data rates for communicating with link partners on a network medium via the physical layer devices. Each physical layer device is automatically prevented from communicating with the repeaters, when a change in the data rate of the physical layer device is detected. Then, status information of the physical layer device is determined, and the physical layer device is enabled to communicate with a selected one of the repeaters having a data rate conforming to the data rate of the physical layer device.
In accordance with one aspect of the invention, a network transceiver comprises one or more physical layer devices having a variable data rate selected depending on the operating speeds of said link partners, and a plurality of busses corresponding, respectively, to the data rates of the repeaters, for interconnecting the repeaters and one or more of the physical layer devices. A multiplexer interconnects each of the physical layer devices to a selected one of the plurality of busses. Handshake logic is responsive to a change in the data rate of a physical layer device for preventing it from communicating with the repeaters until one of the repeaters is ready to communicate with the physical layer device. The handshake logic enables the repeaters to read status information of the physical layer device and change its connection to the repeaters, based on the status information.
In the preferred embodiment, the physical layer devices are configured to perform signal conversion for signal compatibility between the repeaters and the link partners. The physical layer devices each include first transmit and receive channels of a first data rate and second transmit and receive channels of a second data rate. An auto-negotiation unit controls the multiplexer to interconnect each of the physical layer devices to a corresponding bus selected depending on the operating speed of the link partner.
Various objects and features of the present invention will become more readily apparent to those skilled in the art from the following description of specific embodiments thereof, especially when taken in conjunction with the accompanying drawings.